New small chimney to be.

[bernie]

Will be doing this chimney soon and I need some advice. Inside the house will be a wood burning free standing stove, and 90* elbowed into the chimney. The block will be square with the flue liner inside and a total of 12 feet high. My question is .....is there a special mortar for the liner? do i fill the cavity between liner and block? Is there anti-freeze (what kind) I should be using (been in the twentys lately). Does there need to be an access inspection fitting and where and how does it go. Can I just use a 7" mason blade to cut a square hole in liner and is there a special fitting for that entry besides thin black stove pipe? so many questions I ask , and so cold outside , and so hungry I might add. bernie

[Don_P]

Masonry is not my area but I did come across this set of tech notes from the brick institute that looked good.
http://www.gobrick.com/BIA/technotes/t19b.htm

Around here they just use type N to set the flues making the joints very thin. Refractory cement is the right thing though I believe. I've seen a chimney split where the space between the flue liner and the flue block was packed full of mortar in the area where the thimble from a woodstove came in. It couldn't handle the expansion. That chimney has been rebuilt without that feature and seems to be doing fine.

You can buy round clay thimbles for the stovepipe to slip into. They also do make a flue liner with a hole for the thimble already in it, I've not seen them many places though. You can nibble a round hole in the square liner. It needs to go no more than just flush to the inside of the liner. Do not use terra cotta drain tile for any of this, it all needs to be fireclay. Believe it or not, I've seen that on a job.

The whole list of tech notes is here, looks like a good bookmark;
http://www.gobrick.com/BIA/technotes/technote.htm

[bernie]

Thanks Don P for that info .....sure helps.

[justinh]

It would be advantageous to check your local building codes. They vary by state and even county. Some counties require rebar reinforcing with 1/2" rebar in all four corners in the chimney with 24" vertical overlap, drilled and epoxied into a concrete base slab. Outside air is required in many counties as well, so the fireplace doesn't use heated indoor air to burn.

Type N mortar is fine for this application. If you want stronger bond, you can use Type S mortar with a latex bonding agent. This will significantly strengthen the bond and still give flexural strength, as Type S mortar tends to be more brittle than Type N, given it has more cement and less sand/lime.

As for freezing, there are mortar additives you can use, but they only protect down to 15 degrees usually. Fast-Set has been deemed corrosive, so use Hard-N-Fast if you're dealing with freezing temperatures, and insulate the work! Otherwise you may have to tear it out if the frost breaks the mortar's bond!

The bottom of the chimney flue should have an access door for cleaning any fly ash as well as removing chimney sweep residue. It is also recommended to have a chimney cap, especially if it rains frequently in your area.

If you're interested in heating your home for 24 hours from just a two hour fire, visit Mastercraft Masonry's website below!


http://mastercraftmasonry.blogspot.com
Professional Masonry Since 1974
Fully Licensed, Bonded & Insured
Oregon and Washington